The present invention relates to corrosion resistant, electrically non-conductive, ferromagnetic metallic fillers, wherein the metallic filler is protected by treatment of its surface with a triazole, and to compositions containing same. More particularly, the invention relates to polymeric compositions, containing a corrosion resistant filler, which are suitable for use as microwave absorbing materials.
Polymeric compositions containing ferromagnetic metallic fillers are frequently used as materials for microwave absorbing. Such compositions are used, for example, as coatings, gaskets, molded or extruded articles and sheet materials. Various ferromagnetic materials are known, but typically carbonyl iron is preferred, due to its relatively low cost and commercial availability.
Articles, e.g. coatings and gaskets, formed from such compositions are frequently used in harsh environments, in which the metallic filler at or near the surface of the article is subject to corrosion. This causes formation of an oxide layer on the surface of the article which may deleteriously affect the electromagnetic or other properties of the article. Additionally, the oxide layer (e.g. rust) is unsightly and unacceptable to the user. Iron, in particular, is extremely susceptible to rusting.
One approach to this problem has been the use of metal alloys, e.g. iron silicide, as metallic fillers. While these fillers provide improved corrosion resistance, they are significantly more expensive than conventional fillers and typically have inferior electrical properties.
Thus, it has been desired in the microwave absorbing field to provide polymeric compositions which would not be susceptible to corrosion, even under extreme environmental conditions.